Beau Biden, 46, of Greenville, Del., was undergoing treatment Tuesday at Walter Reed National Military Medical Center in Bethesda, Md, the vice president's office confirmed. But the office offered no details on Beau Biden's condition or what caused him to seek treatment.

Attempts to contact Joe Biden's office and a Beau Biden spokesman Wednesday for updates went unanswered. A Walter Reed spokeswoman said hospital policy is not to offer any information about patients because of privacy laws.

"I'm very concerned," said Tom Gordon, New Castle County executive, a friend and political ally of the Bidens. "That's all I care about. I've known him all his life. I'll be praying that he's fine."

Biden has withdrawn from the public spotlight since an August 2013 operation at the University of Texas M.D. Anderson Cancer Center in Houston to remove a small brain lesion. Biden served two terms as Delaware attorney general and told supporters last year he would launch a 2016 campaign to become Delaware's next governor.

Even during his final months as attorney general, Beau Biden offered very little public comment and avoided interviews and public events.

Beau Biden timeline

• 1994. Graduates from Syracuse University College of Law in New York.

• 2002. Marries wife, Hallie; they later have children Natalie and Hunter.

• 2003. Joins Delaware Army National Guard and still serves.

• 2006. Elected Delaware attorney general, his first run for public office.

• 2008. Deploys to Iraq for almost a year.

• May 2010. Suffers what was called a mild stroke.

• November 2010. Elected to second term as Delaware attorney general.

• August 2013. Has surgery to remove brain lesion.

• November 2013. Given a clean bill of health.

• April 2014. Announces he will not run for a third term as attorney general, instead saying he will run for Delaware governor.

• January 2015. Joins Grant & Eisenhofer law firm in Wilmington.

• May 2015. Hospitalized in Bethesda, Md., for undisclosed ailment.

• May 30, 2015. Died from brain cancer.

Source: USA TODAY research

He left office when his term was up in January, accepting a position at the Wilmington law firm Grant & Eisenhofer.

Beau Biden had been keeping a low profile by design, said Timothy Mullaney, Beau Biden's former chief of staff who is expected to help with a gubernatorial campaign.

"I didn't anticipate we were going to do anything until this summer," said Mullaney, who spoke to Beau Biden within the past month and met with him several weeks ago. "Last time we talked he was fine. There was nothing that was going to stop him from running."

Almost two years ago, Beau Biden sought treatment in Houston after becoming weak and disoriented on a family vacation. In November 2013, three months after his procedure, doctors gave him a clean bill of health, according to a statement that M.D. Anderson hospital issued last year.

The 2013 incident was not Beau Biden's first health scare. In May 2010, he suffered what was described as a "mild stroke."